°)45 







m 



UNITED STATES DEPARTMENT OF AGRICULTURE 



m BULLETIN No. 273 

*^^|><<L1^? Contribution from the Bureau of Entomology *>J 

^^*^^U L. O. HOWARD, Chief S^^^'^^^U 




IWashington, D. C. 



PROFESSIONAL PAPER 



August 24, 1915. 



DISPERSION OF GIPSY-MOTH LARV^ BY THE 

WIND/ 

By C. W. Collins, 
Entomological Assistant, Gipsy Moth and Brown-tail Moth Investigations. 



CONTENTS. 



I Previous investigations : Page. 

On dispersion 2 

Of hairs on small larvae 3 

I Studies of acuminate and vesicular hairs 4 

jScope of investigations 6 

JHatehing in relation to wind dispersion 7 

I Longevity of entrapped first-stage larvae 8 

I Screen experiments 8 

[Dispersion experiments, New Hampshire 

hills 14 



Altitude experiment 15 

Observations on wind dispersion 17 

Observations for reinfestation 17 

Small larvae blown into ocean 18 

Feeding prior to dispersion 19 

Comparison of weather data 19 

Spread of gipsy moth 20 

Summary 21 

Bibliography 22 



INTRODUCTION. 

The territory infested by the gipsy moth {Porthetria dispar L.) is 

[gradually increasing in area, and since isolated colonies are being 

found each year in woodlands and orchards remote from lines of 

kravel, the question as to then origin has become more urgent. 

Many agencies assist in the transportation of the moth in its various 

stages, but as previous experiments proved that small caterpillars are 

borne by the wind, it seemed desirable to ascertain to what extent 

[this occurs and the maximum distance they may be blown under 

I field conditions. Much depends upon this factor in diffusion, when 

devismg methods of preventuig the spread of this pest, and as a 

I practical result of previous experiments tanglefoot has been used 

extensively in colonies located in the outside infested towns. Ti'ees 

are banded with tanglefoot to prevent the small larvae from ascending 

to the tops, and thus the chances that these larvae will be blown 

long distances are decreased. 

1 An extended report on one of the important phases of gipsy moth control work, conducted under the 
direction of the Biu-eau of Entomology, L. O, Howard, Chief, and in cooperation with the various 
States affected. 

968io°-Buii. 273-15 — 1 Mooograph 



2 BULLETIN 273, U. S. DEPARTMENT OF AGEICULTURE. 

To secm-e further information, the writer, under the direction of 
Mr. A. F. Burgess, commenced a series of experiments in the spring 
of 1913 and continued them throughout the following year.^ 

PREVIOUS INVESTIGATIONS ON DISPERSION OF THE GIPSY MOTH. 

Many mvestigations of various sources of spread of this insect were 
conducted during the early nineties by Forbush and Femald and 
pubhshed by the Massachusetts State Board of Agriculture in 1896. 
It was found that frequent teamuig in and out of the origmal infested 
areas (Medford, Boston, and towns closely surroundmg) by vehicles 
transportmg larvse that dropped from infested shade and roadside 
trees was largely responsible for the general local spread during those 
years. It was also suggested that the larvae were occasionally trans- 
ported by the wind to distances of perhaps 100 yards, but no further 
observations were made at that time to substantiate this theory. 
Numerous ways and means of local spread, such as by birds, animals, 
and man, are treated m this valuable report. 

In the sprmg of 1910 Mi\ A. F. Burgess began a series of experiments 
on dispersion of the gipsy moth the account of which is pubhshed as 
Bulletin 119 of the Bureau of Entomology. A few small experiments 
were made in the laboratory by releasmg silk-suspended first-stage 
gipsy-moth larvas in front of an electric fan, and it was found that 
they soared to a distance of 20 to 30 feet in the air before ffdling. 
This led to more extensive experiments conducted under out-of-door 
conditions. Screens constructed of poultry wire and covered with 
tanglefoot were stationed at given distances from sources of infesta- 
tion and watched for catches of larvae. On a small screen stationed 
on the marshes near Lynn, Mass., newly hatched larvae were caught 
that had been carried 1,833 feet by a west wuid at a velocity of 7 to 
19 miles per hour. 

Numerous records were compiled to show the relation of tempera- 
ture, wind velocity, and wuid direction to the general trend of spread 
as it has progressed from the original center, Medford, Mass. It was 
clearly demonstrated that the prevalent southwest winds following 
the hatching period of the eggs each year has resulted in the more 
rapid dispersion of the moth to the northeast than m any other direc- 
tion. Large woodland areas were scouted m various towns, the 
data of which were compiled and show the extent to which tlie wuid 
is responsible for the remote and numerous colonies located. The 
automobile is also included in this report, as a very important factor 
in carrying the caterpillars both locally and for long distances. 

1 The writer is indebted to Mr. L. H. Worthley and Dr. J. W. Chapman for cooperation and helpful 
suggestions; to Messrs. C. E. Hood, F. W. Graham, and Harry lilaisdell for the collection of field data; 
to Mr. H. A. Preston for the preparation of photographic illustration-:, and to others oi the laboratory 
iorce who contributed in various ways. 

D. oi! D. 
SEP ^i 1916 



(5 V^ 
CS^^ DISPEESION OF GIPSY-MOTH LARV^ BY THE WIND. 



&^^ 



FORMER INVESTIGATIONS OF HAIRS ON SMALL LARV^. 



The bodies of first-stage laiTse (PI. I, fig. 1) are pi'ovided both, 
dorsally and laterally with two types of hairs, or setse, namely, short, 
smooth hairs bearing a vesicle about the middle and very long, slender 
ones which are covered with spinules. Wachtl and Komauth in 
1893 first described the aerostatic seta? fomid on the first-stage 
larvse of P. dis'par L. and Lymantria rnonacJia L. and designated 
the bdHoon-shaped swellings occurring on these setae as aerophores. 
They suggest that these aerophores assist ui the dissemination of the 
young caterpillars through the air. 

Prof. Cholodkovsky in 1894 made some investigations and found 
that the swelhngs or vesicles shrank in dead larvae. His discovery 
tended to weaken the theory that these swellings contam air and to 
suggest that they may contain a fluid which will naturally dry up 
after death. He also fomid that the sweUings remained for months 
in alcohol as full and rounded as m hvuig lai-vae, and if the preparation 
was allowed to dry on a shde the aerophores quickly shriveled. 
He therefore concluded that they did not contain air but a fluid 
which was probably poisonous and served as a protection against 
insectivorous birds. 

Igenitzky, a student of Cholodkovsky, in 1897 further studied the 
glands that give rise to the hairs and verified the findings of the former 
investigator, who proposed to call the sweUings " toxophores. " He 
further states that the role of rendering the larvae more buoyant may 
better be ascribed to the long thin hairs which resemble the pappus 
of some plant seeds. 

Prof. K. Escherich in 1912 published a resume of former investiga- 
tions into the function of the hairs and cites later work by Wachtl and 
Kornauth in 1907 in which they cling to their former theory of aero- 
phores. The latter found that the vesicles did not contain liquid, as 
no reaction was noted by immersion in litmus, rosolic acid, or phenol- 
phthalein, indicating that they contained neither, alkali nor acid. 
They did not shrink in alcohol, glycerin, or acetic acid, or excite any 
capillary action; hence the mvestigators concluded that nothmg but 
air could be contained in them. Prof. Escherich lays stress on the 
air refraction noted in connection with these balloons when immersed 
ia glycerin and viewed under the microscope. 

T. C. Shcherbakov in 1914 published observations on the gipsy 
moth in which he deals at length with the function of the hairs on the 
first and second stage larvae, and parts of his paper have been trans- 
lated by Mr. J. Kotinsky of the Bureau of Entomology. Shcher- 
bakov says that the aerophores are not filled with air or gas and that 
their connection with the glandular cells would indicate that these 
vesicles are probably filled with a poisonous secretion. Their exceed- 



4 BULLETIN 273^ U. S. DEPARTMENT OF AGRICULTUEE. 

ingly small size, he contends, makes them physically inadequate to 
sustain the caterpillar in the air. On the other hand, the very numer- 
ous, very long hairs which cover the larva, in addition to the wonder- 
ful amount of silk it is capable of spinning, point to the general 
morpho-physiological structure as the factor enabling it to soar. 

He compares this ability of the caterpillar with the meaning of 
soaring as this term is used by V. N. Chitrovo in an epoch-making 
botanical work on the study of weeds.^ Soaring is the capability of 
a body passively to participate in an air current, as if constituting 
part of it, arising from special characters in the structure of the body. 
The analogy in function between the wmd-borne seed and caterpillar 
is complete. 

Soaring is determined by the coefficient calculated by the following 

formula: 

^_ /(cm-) 
w(gr) 

where C is the soaring coefficient; /, the surface area (in square cm.); 
and w, the weight (in grams) of the caterpillar. The coefficient of a 
bare, freslily hatched first-stage caterpillar is 514.285 and Shcher- 
bakov says that it would be more than six times as great if the area 
of the hairs were included. 

Compared with the Chitrovo soaring table of seeds, the coefficient 
for the first and second stages of the caterpillar places them among 
the greatest seed soarers. In a slight wind these caterpillars are 
capable of soarmg. The distance they can cover depends on the 
topography of the country, the character and abundance of vegeta- 
tion, the mobility of the caterpillar which in turn depends upon the 
temperature of the atmosphere, and the availability of foods. The 
soaring coefficient diminishes sharply for caterpillars in the second 
stage. 

This investigator also states that G. G. Jacobson once, while trav- 
eling, observed caterpillars flying in masses toward him, despite the 
fact that he was at least 17 miles away from the nearest forest. 

STUDIES OF STRUCTURE AND FUNCTION OF ACUMINATE AND VESICU- 

LAR HAIRS. 

Owing to the differences of opinion existing as to the structure and 
function of the hairs covering the bodies of first-stage larvse, the 
\ATiter and Mr. C. E. Hood, with the assistance of Dr. J. W. Chapman, 
made some tests during the winter of 1914-15. The aim of these 
experiments was to study both the long acuminate hairs and the short 
ones bearing vesicles. As the results differ somewhat from those of 

1 Atlas von Samen und Friichten der Feldunkraiiter aus Mittelmssland. Bui. fiir angewandte Botanlk, 
wissenschaftliches Organ des Bureau fiir angewandte Botanik (Monatsschrift), Jahrg. 7, no. 3, 118 p., 16 
fig., 13 pi., March, St. Petersburg, 1914. 



Bui. 273, U. S. Dept. of Agriculture 



Plate 




Fig. 1. -First-Stage Larva Showing Two Kinds of Hairs. (From Burgess.) 




Fig. 2.-a, Tubercle from First-Stage Larva Showing Hairs; b, Vesicular 
Hairs; c, Acuminate Hairs. All Much Enlarged. 'Original.) 

GIPSY-MOTH CATERPILLAR SHOWING VESICULAR AND ACUMINATE HAIRS. 



DISPERSION OF GIPSY-MOTH LAEV^ BY THE WIND. 5 

previous investigators in that the swellings on the short hairs were 
found to contain a liquid not yet proven to have toxic properties, it 
seems advisable that they should hereafter be called vesicular hahs. 
(PI. I, fig. 2, &.) The term "aerophore" previously applied to the 
swellings on the short hairs is misleading, as is also the tenn "toxo- 
phore" suggested by Cholodkovsky. The term "acuminate" stdl 
applies to the very long slender hahs. (PL I, fig. 2, c.) 

After first-stage larvae die the sweUmgs on the hairs usually col- 
lapse and both air and liquid are present in each tjrpe of hair and can 
be seen under a high-power microscope. A living caterpillar exam- 
ined in glycerin shows air bubbles occasionally in the hahs and 
swellings which sometimes extend above and below the latter. The 
air globules and liquid columns alternate m hairs of dead larvee, and 
the difference between the air or colorless liquid present is evident from 
the typical air refractions in the globular form that air always takes 
in a liquid; also from the capillary attraction of the liquid contamed. 
Living caterpillars mounted in balsam and examined under a micro- 
scope show air bubbles in some of the hairs, but such hairs are excep- 
tions rather than the rule. Caterpillars that have been dead several 
days show the opposite phenomenon — both air and liquid are seen in 
them, but air predommates. Some larvae that had been dead for 
two years were examined and these contained small short columns of 
liquid, but air filled the greater portion of the hollow spaces of the 
hairs. Practically the same was noted m the hairs of an exuvium 
from a first-stage larva which had also been kept about two years. 
The vesicles on the hairs had buckled or collapsed and contained air, 
which was later practically all driven out by heating. 

Embryos were dissected from the chorion under balsam and 
glycerin and then examined in these media. No air globules or 
what could be termed air refractions were noted in either acuminate 
or vesicular hairs. Many of the vesicles are only partially distended 
in tliis stage. Embryos dissected from the chorion in air contained 
air globules and columns of fiquid alternating in a portion of both 
types of hairs — ^probably those ruptured during the dissection. 

After some experience it is easy with the aid of a high-power 
miscroscope to recognize the difference in refractions tlii'ough the 
walls of hairs full of colorless liquid or containing globides of air and 
columns of fiquid alternating. The typical fiquid refractions are 
always seen in uninjured vesicular and acuminate hairs. Only 
rarely are there air refractions noted in either type on living larvae. 
A decided change in aspect is noted in dead larvae after the vesicle 
begins to collapse, at which time air finds its way into the hairs. 

A number of fiving larvae were placed under a beU jar wliich con- 
tained a small amount of concentrated sidphuric acid. After six 
hours many of the larvae were dead and upon examination a large 



6 BULLETIN" 213, U. S. DEPARTMENT OF AGRICULTUEE. 

portion of the vesicles of the haii-s had buckled or partly collapsed. 
Larvae still living at this time presented the same appearance to a 
slight extent. As a check on this experiment, larvse were killed with 
cliloroform and after 24 hom-s showed a smaller pro2:)ortion of buckled 
or collapsed vesicles, indicating that sulphuric acid took up moisture 
from the porous hairs. 

Sections were made of the larvaG and cells at the base of the 
hairs studied, but there coidd be found no indication of the presence 
of glandular cells. A large trichogen, however, is present at the base 
of each hair. This would signify that the liquid inclosed in the 
hairs is not a toxin, as Cholodkovsky suggests, but a mere colorless 
mobile hquid secreted diu-ing the formation of the hairs. The 
phenolphthalein and litmus-solution tests were also tried, with nega- 
tive results, further indicating a neutral liquid. The peculiar shape 
of the vesicular hairs, however, suggests that they may at one time 
have had a poisonous function but that it has been lost in the present 
generations. 

The results of the experunents and observations indicate that both 
the normal vesicular and acmiiinate haire are idled with a colorless 
liquid; that the hairs are hollow throughout, and that the vesicles 
contain the same media as the remaining portion of that type. A 
few globules of air were seen in hairs of living larvae wliich were no ted 
as exceptions. Air partially replaces the liquid after death, following 
which period the vesicles collapse. It is therefore probable, as Ige- 
nitzky and Shcherbakov have indicated, that the acuminate hairs 
play the greater role in making the larvse more buoyant, as these 
are from four to six times as long as the vesicular hairs. 

SCOPE OF INVESTIGATIONS ON WIND DISPERSION. 

In that the main purpose of the following investigations was to 
secm*e data on the maximum distance and the extent to which small 
larvae are borne by the wind, it was necessary to find conditions 
where an abundance of larvae were present in close proximity to 
treeless areas. These conditions were best afforded along the beaches 
in Massachusetts and New Hampshire, where there are stretches of 
marehland from 1 to 2^ miles wide and many miles long. These 
marshlands are occasionally flooded with salt water and do not con- 
tain vegetation favorable to the development of gipsy-moth larvae. 
The areas selected for the experiments were to the east of the heavy 
infestations, thereby getting all the advantages previously known to 
accrue from the northwest, west, and southwest winds. The Isles 
of Shoals, off the coast of New Hampsliire, afforded ideal conditions 
in so far as their remoteness from the mainland was concerned and 
the fact that the country opposite has been infested since 1905. 
Locations were also selected in the liills of New Hampsliire near the 



DISPERSION OF GIPSY-MOTH LAKViE BY THE WIND. 



quarantine line for experiments intended to explain the sources of 
many infestations found under such conditions. 

Screens of poultry wire, to which tanglefoot was applied, were 
erected in three of the selected locations along the coast and on the 
Isles of Shoals (PI. II). Those used in the New Hampsliirc liill ex- 
periments were of a somewhat different type and are described 
xmder that head. The screens used along the coast (PI. Ill, fig. 1) 
were of ^-inch mesh poidtry wire stapled to 2 by 4 posts which 
were set in the ground and held in place at the top by guy wires and 
wooden braces. The posts were 12 feet high and two sections of wire 
each 75 feet long and 3 feet wide were fastened to these so that the 
top selvage was 12 and the lower 6 feet from the ground. The 
screens contained 450 square feet of wire and were built in three 
25-foot sections, the middle section facing the west and the other 
two anghng from tlie ends about 45° to the eastward. This gave 
the greatest exposure at all times to the northwest, west, and south- 
west winds. A runway was attached to the posts at the bottom 
selvage of the wire to facihtate examinations. 

HATCHING OF EGGS IN RELATION TO WIND DISPERSION OF FIRST- 
STAGE LARV^. 

Close observations on the time of hatcliing of egg clusters in the 
field have been kept since 1912 by laboratory men stationed in 
different sections of Massachusetts and New Hampshire. The data 
consulted were collected by Messrs. E. A. Proctor in northeastern 
Massachusetts, J. V. Schaffner, jr., in Massachusetts south and south- 
west of Boston, and I. L. Bailey in south-central New Hampshire. 

Table I. — First, maximum, and last dates of hatching in 1912, 1913, and 1914- 



Year. 


Northeastern Massachusetts 
hatching. 


Southeastern Massachusetts 
hatching. 


South-central New Hamp- 
shire hatching. 


First. 


Maxi- 
mum. 


Last. 


First. 


Maxi- 
mum. 


Last. 


First. 


Maxi- 
mum. 


Last. 


1912 

1913 


Mav 2 
Apr. 25 
May 11 


May 11 
May 5 
May 15 


May 22 
May 27 
May 28 


Mav 1 
Apr. 26 
May 9 


May 15 
May 10 
May 15 


May 25 
May 21 
May 23 


May 1 
Apr. 29 
May 11 


May 14 
May 8 
May 16 


May 23 
May 14 


1914 


May 28 



The first larvse were caught on the screen in northeastern Massa- 
chusetts May 9, 1913, and the last June 5, while the largest numbers 
were removed between May 14 and Jmie 1. During 1914 in the 
same section the first larva was caught about May 16, while the 
largest numbers were removed from May 20 to May 27 and the last 
June 6. One larva was caught in Hemiiker, N. H., as late as June 
13, 1914. 

In a year of normal hatching, as in 1913, wind dispersion was 
noted about two weeks after first hatching and one week after hatch- 



8 BULLETIN 273, U. S. DEPARTMENT OF AGRICULTURE. 

ing was completed. In 1914 there was an abnormally late spring, 
which shortened the hatchmg season, and wind dispersion was noted 
about one week after the first date and continued about the same 
period after the last was observed. The total period over which 
wmdspread may be expected is from 27 to 30 days m a normal 
spring, and from 18 to 20 days during a late spring. Ordinarily the 
maximum dispersion is effected durmg 10 to 15 days of high tempera- 
tures and favorable winds. 

LONGEVITY OF FIRST-STAGE LARV^ AFTER BECOMING ENTRAPPED IN 

TANGLEFOOT. 

In connection with the experiments conducted by using tanglefoot 
on screens to catch caterpillars blown by the wind, it became essential 
to know about how long they would live after becoming entangled. 
As a test, tanglefoot was smeared at various depths on heavy paper 
and 100 caterpillars dropped into these. Exammations were made 
at intervals from the time the experiment was started, and it was 
noted that after three hours practically aU were living; after six 
hours only two were attemptmg to move, and these were in a very 
thin smear. After eight hours 65 were dead, and 35 showed signs of 
life when disturbed. The following morning, after 24 hours, aU were 
dead except seven, and these were in very thin smears, which had 
little effect upon them. 

The length of life depended upon the density of the tanglefoot in 
which they were placed. If the caterpillars m attempting to free 
themselves became submerged below the spiracles, which often hap- 
pened in 3 to 5 hours, they died shortly after. As a result, cater- 
pillars lodged in globules of tanglefoot on the screens died in 4 to 6 
hours, while those in very thin spots lived 24 or more. 

SCREEN EXPERIMENTS AT SALISBURY BEACH, MASS., IN 1913. 

April 24, 1913, a large screen (PL III, fig. 1), as described, was 
erected on the edge of the marsh area near the beach, on a site which 
was 1 mile distant from infested woodlands to the northwest, IJ 
miles to the west, and 2 J miles to the southwest. The area to the 
east, composed of sand dunes, contained small amounts of vegetation, 
on which gipsy moths could thrive, but this was properly scouted 
and cleaned for an experiment on reinf estation by the wind. 

The temperature, wmd direction, and wind velocity were taken 
each day at alternate hours from 9 a. m. to 5 p. m., and the screen 
was examined most days when the winds were fair for windspread 
from the west. Mr. F. W. Graham was in attendance at this screen 
and made many of tlie following observations and notes. 

No larvae were blown on the screen, which was one-fifth mile from 
the ocean, by wmds coming directly from the east. Larvae were 



Bui. 273, U. S. Dept of Agriculture. 



Plate II. 




MAP 

showing 
LOCATION «■ SCREEN TFtAPS 
where 
GIPSY MOTH LARVAE 
were eaii^t In 1013 ■-> 1014. 



Map Showing Location of Screen Traps where Gipsy-Moth Larv^ were 
Caught in 1913 and 1914. 



Bui. 273, U. S. Dept. of Agriculture. 



Plate III. 



. • A 


vj^a- 


1 




1--^^^ 






„.jBfc«» — .« mum*' 


■RMMHMnva^ - 
















•~ A . 



Fig. 1.— Screen at Salisbury Beach, Mass., where 266 Larv/e were Caught 
During May and June, 1913, and 96 in May, 1914. Showing Beach and 
Ocean in Background. (Original.) 




Fig. 2.— Screen at Plum Island, Mass., where 42 Larv/e were Caught in May, 
1914. Newburyport in Background 2 Miles West— Nearest Infested Tree 
Growth in that Direction. (Original.) 



SCREEN TRAPS FOR WIND-BLOWN GIPSY-MOTH LARV/E ON 
MASSACHUSETTS COAST. 



DISPEESION OF GIPSY-MOTH LARV^ BY THE WIND. 



9 



borne, however, by northeast and southeast winds from beach infes- 
tations 1 mile or more distant. This screen was inspected in May by 
Dr. Howard and Dr. Paul Marchal. 



Table II. — Dates and numbers of newly hatched caterpillars caught on screen, ivith tem- 
peratures, direction of wind, and velocity of tvind, at Salisbury Beach, Mass., in 191S. 



Date and time removed. 



Number of 
caterpil- 
lars caught. 



Maxi- 
mum 
temper- 
ature. 



Minimum 
tempera- 
ture. 



Average between 9 a. m. 
and 5 p. m. 



Prevailing 
wind direc- 
tion. 



Wind veloci- 

ity, in miles 

per hour. 



May 9, p. m 

May 10 , 

May 11, a. m 

May 12 

May 13 

May It, a. m 

May 15, a. m. and p..m 

May 16, p. m '. . . 

May 17, p. m 

May IS 

May 19, p. m 

May 20, p. m 

May 21, p. ra 

May 22 

May 2.3, p. m 

May 24 

May 25 

May 23, p. m 

May 27 

May 28 

May 23 

May 30, p. m 

May 31, p. m 

Juiic 1, a. m. and p. m. 

June 2, p. m 

June 3, p. m 

June 4, p. m 

Junes, p. m 

Total 



(') 
(0 



(') 



0) 



(0 
(0 

(1) 



(}) 



(?) 



S.andSE... 
W. andSW. 

NW 

NW 

NW.andSE 

SW 

NW 

W. and SW. 

NE 

E. and NE.. 



11 to 15 
8to U 
18 to 22 
15 to 18 
8 to 11 
10 to 13 
13 to 17 

7 to 9 

8 to 12 
8 to 12 



W. and NW 
NW.andW. 
SE 

E.toNw!!! 
NW. SW., 
and E. 

N. to E 

E . and SE . . 
NW to E . . . 
E 

n:: 

NW 

W.andNW. 
NE to NW . 
SE toSW... 

NW 

SW 

NW. toE... 
E.toS 



18 to 23 

15 to 20 
8 to 12 

6 to 8 
2 to 5 

7 to 10 

7 to 11 

6 to 10 

8 to 12 
8 to 11 

19 to 23 
17 to 21 

8 to 12 

16 to 20 
16 to 20 
15 to 19 
12 to 16 

7 to 11 



1 No examination. 



- No records. 



It wiU be noted from Table II that 266 caterpillars were caught on 
450 square feet of wire, and most of these on days when the winds 
blew from the northwest, west, or southwest, namely, May 14 to 19, 
May 15 to 17, May 19 to 25, May 20 to 30, etc., while fewer were 
caught when the wind was from the northeast and southeast. This 
may be explained by the light infestations 1 mile or more to the north- 
east and southeast; also it will be noted that winds from these direc- 
tions along the coast are accompanied by much lower temperatures, 
at which time the caterpillars spin less actively. 

Many of the small larvee were taken on the posts and crosspieces of 
the structure; thus of the 25 caught May 19, 18 had lodged in this 
manner and were living when removed. Others were swinging by 
threads on the east side of wire, where they had blown through the 
mesh from the west, the threads having caught in tanglefoot. 
96810°— Bull. 273—15 2 



10 



BULLETIN 273, U. S. DEPARTMENT OF AGRICULTUKE. 



The first larva was caught May 9 and the last June 5, although 
exammations of later date were made. These dates indicate the 
range of the wind dispersion period for that section in 1913. The 
distance borne by the wmd was 1 mile or more. 

Another small experiment was conducted 200 feet from the above 
screen by attaching to the northwest, west, and southwest sides of a 
small stable 77 square feet of cotton cloth which was smeared with 
tanglefoot. This experiment was not started at the beginning of 
the season, but larvae were blown into the tanglefooted cloth be- 
tween May 20 and 31. The object in this experiment was to ascer- 
tain the comparative efficiency of tanglefooted wire screen and a solid 
tanglefooted surface as traps. 

CONTINUATION OF SCREEN EXPERIMENT AT SALISBURY BEACH, MASS., 

IN 1914. 

The same screen (PL III, fig. 1) as was erected in 1913 was cleaned 
and retanglefooted for the dispersion season of 1914. The infesta- 
tion in the woodlands to the westward, owing to the increase of 
Calosoma sycophanta L., Com.psilura concinnata Meig., and the wilt 
disease, was less intense during the latter year. The dispersion 
period was much later and consequently much shorter than in 1913. 
Examinations were begun about the time the hatching of eggs was 
first noted in the field. The first caterpillar was caught May 19 and 
the last May 31 in this location. 

The weather records were taken 1 mile south for this point at Plum 
Island, Mass. (PL II), by Mr. C. E. Hood, and were compared with 
those of the United States Weather Bureau at Boston, Mass., from 
which they differed very little. 

Table III.^ — Dates and numhers of newly hatched caterpillars caught on screen, with tem- 
perature, direction of wind, and velocity of wind, at Salisbury Beach, Mass., in 1914- 



Date and time removed. 



Number 
of cater- 
pillars 
cauglit. 



Maxi- 
mum 
tempera- 
ture. 



Mini- 
mum 
tempera- 
ture. 



Average between 8 a. ra. and 
5 p. m. 



PrevaLUng wind 
direction. 



Wind veloc- 
ity, in miles 
per hour. 



May 19, a. m 

May 20, a. m 

May 21, a. m. and p. m 

May 22, a. m 

May 23, a. m. and p. m 
May 24, a. m. and p. m 

May 25, a. m 

May 2r), a. m 

May 27, a. m 

May 28, a. m 

May 29, a. m. and p. m 

May 30, a. m 

May 31, a. m. and p. m 

Total 



"F. 



°F. 



W. and NW... 
W. andNW... 

NK. toSE 

E.andSE 

W 

W 

sw 

SW.and W...- 

W.toS 

NW 

E.andSE 

SW 

W 



8 to 12 
2 to 6 
7 to 11 
2 to 10 

10 to 23 

11 to 16 

12 to 21 
7 to 20 
4 to 12 

11 to 20 

9 to 17 
7 to 9 
7 to 14 



DISPERSION OF GIPSY-MOTH LARV^ BY THE WIND. 11 

In all 96 larvse were trapped during tlie season, most of which 
were removed on days when the wind blew from the west, southwest, 
or northwest. The largest catch was removed May 21, at wliich time 
the wind blew from the northeast and southeast, but it was evident 
that most of the larvae were caught May 20 in the afternoon, as the 
screen was not examined durmg that period. There was less source 
of spread from the northeast and southeast along the ocean shore 
than from the westward points. On May 21 the temperature ranged 
from 53° to 60° F., at which time there was reasonable activity among 
the caterpillars. 

One should not fail to note that spread was secured from all direc- 
tions from which the wind blew except from the east, and the in- 
festation at this point Was almost obliterated. No north winds 
were noted during the hourly observation periods. 

SCREEN EXPERIMENT CONDUCTED ON PLUM ISLAND, MASS., IN 1914. 

April 14, 1914, a screen (PL III, fig. 2) was erected on the edge 
of the marsh near the Merrimac River. It was of the same size and 
proportions as that erected 1 mile farther north, at Salisbury Beach. 
The slirubbery, composed mostly of beach plum, bayberry, wild rose, 
sumac, poplar, and wiUow, on the north end of the island, was ex- 
amined for egg clusters and these were creosoted. This practically 
obliterated the source of infestation to the eastward of the screen. 

The location of the screen (PL III, fig. 2) was such that it was 2 
miles from infested woodlands across the marshes and Merrimac 
River to the northwest, west, and southwest. Frequent examina- 
tions made it possible to determine the direction from which all the 
caterpillars came. It is not supposed that all the caterpillars caught 
during the time west winds prevailed came from the nearest infesta- 
tions (2 miles), but in some instances 5 miles or more. There was, 
however, a small infestation on a few roadside willows 1 mile to the 
southwest, but these were so thoroughly cleaned and tanglefooted 
in the spring that no caterpillars could be found on them during the 
dispersion season. The woodland infestation was 1 mile bej^ond 
this, totaling 2 miles from the screen. 

Mr. C. E. Hood attended the screen, making three or four exami- 
nations for larvse daily from May 10 to June 13. The temperature, 
wind direction, and wind velocity were recorded hourly each day 
from 8 a. m. to 5 p. m., inclusive. 



12 



BULLETIN 273, U. S. DEPARTMENT OF AGRICULTUEE. 



Table IV. — Bates and numbers of newlii hatched caterpillars caught on screen, with tem- 
peratures, direction of wind, and velocity of wind at Plum Island, Mass., in 1914. 



Date and time removed. 



May 20, a. m. and p.m.. 

May 21, a. ra 

May 22, a. m 

May 23, a. m. and p. m.. 
May 24, a. m. and p.m.. 
May 25, a. m. and p. m.. 

May 26, p. m 

May 27, p. m 

May 28, p. m 

Total 



Number of 

caterpillars 

caught. 



Maximum 
tempera- 
ture. 



Minimum 
tempera- 
ture. 



Averacre between 9 a. m. 
and 5 p. m. 



Prevailing 
wind direc- 
tion. 



"Wind veloc- 
ity, in miles 
per hour. 



AV.andNW. 
NE. toSE., 
E. and SE.. 

AV , 

AV 

SAV 

SAV. and W 
AV. toS.... 
NAV 



2 to 6 
7 to 11 
2 to 10 

10 to 23 

11 to 16 

12 to 21 
7 to 20 
4 to 12 

11 to 20 



A total of 42 caterpillars were removed from this trap between 
May 20 and May 28 — a very short season in comparison to the 
records at Salisbury Beach in 1913. Five of these larvae Avere 
bloAvn on the screen by winds from the east and south, while the 
remaining 37 came with the winds from the Avest. Larvae were 
caught during the morning of May 20, when the velocity of the wind 
for that period ranged from 2 to 4 miles per hour, and on the follow- 
ing day, when the temperature ranged from 53° to 60° F. 

SCREEN EXPERIMENT ON ISLES OF SHOALS, N. H. 

The Isles of Shoals (PI. II), located 6 miles off the coast of New 
Hampshire and Elaine, was selected as an ideal place in Avhich to 
establish a trap for tests in long-distance spread. An elevated spot 
on Appledore Island Avas chosen and a screen erected in April, 1913. 
It Avas not known at that time that Appledore, comprising about 
100 acres, was infested, but subsequent scouting in the summer 
shoAVod that this Avas the case. This island contains a varied groAvth 
of low shrubbery, some of which is very favorable food for gipsy- 
moth larvae, but the infestations were slight and covered small areas 
well scattered over the territory. 

The screen was examined at intervals during that year from 
May 1 to June 3 and 14 first-stage larvae were removed during that 
period. Some of these larvae were alive on removal and Avere taken 
on days when the Avind blcAV directly from the mainland, Avdiich 
indicated that many of them came from that source, hue there Avas 
room for question because the island on Avhich the screen Avas located 
in 1913 was later found infested. 

To eliminate any possibility of error in drawing conclusions another 
island in this group, namely, Lunging, was selected for the experi- 
ment in 1914. It is the most western of the isles and located so as to 



Bui. 273, U. 5. Dept. of Agriculture. 



Plate IV. 




Fig. 1.— Screen on Lunqinq Island, Isles of Shoals, N. H., on which 57 Larv/e 
WERE Caught During May, 1914. Ocean in Background. Vegetation in 
Foreground is Unfavorable Food for the Larv/e. (Original.) 




Fig. 2.— Screen on Holts Hill, Henniker, N. H., where Two Larv/e were 
Caught in 1914. (Original.) 



SCREEN TRAPS FOR WIND-BLOWN GIPSY-MOTH LARV/E IN NEW 

HAMPSHIRE. 



DISPERSION OF GIPSY-MOTH LAEV^ BY THE WIND. 



13 



receive the full force of the northwest, west, and southwest wmds 
directly from the mainland. This island is composed mostly of bare 
rock, with small patches of soil. There is little favorable vegetation 
for gipsy-moth larvae, and three careful examinations made in the 
spring of 1914 revealed no egg clusters. 

Four hundred and fifty square feet of wire screen was used, and 
an extra screen was made of cotton cloth tacked to a frame 40 feet 
long and .3 feet wide, and tanglefoot apphed. It was anchored at 
an incline on the rocks, facing the west. 

On this island there is one cottage which afforded quarters for 
Mr. Harry L. Blaisdell, who was in constant attendance at the 
screen (PI. IV, fig. 1). Arrangements were also made with the 
United States Life-Saving Service for transportation to and from the 
islands on their regular trips to Portsmouth, N. H. Mr. Blaisdell 
recorded the weather conditions hourly from 8 a. m. to 5 p. m., using 
a compass, thermometer, and hand anemometer. He also examined 
the screens continuously and made careful notes on the time and 
wind conditions when each caterpillar was caught, which made it 
possible to detemiine the source from which it came. Practically 
all the larvae found on the screens were alive, and in most cases they 
were removed very soon after entanglement. 

Table V. — Number of caterpillars caught at Lunging Island, Isles of Shoals, N. H., in 
1914, icith direction ajid distance from xchich they came. 



Date. 


Other islands 
of the Isles 

of Shoals, E., 
NE., SE., 

and S., Jand 
g mile. 


Kjttery, Me., 
NW., 7 miles. 


Wallis Sands 
and Rye, 

N. h:, 

WNW., 6 
miles. 


Rye Ledse 

and Little 

Boars Head, 

N. II., W., 

7 miles. 


Seabrook, 
New Hamp- 
shire, and 
Ma=:sachu- 
setts line, 
WSW.,11 
miles. 


Plum Island 

(north end), 

Mass., SW., 

13i miles. 


1914. 
May 20 


6 
6 

1 


1 










May 21 










May 22 












May 23 




8 
20 


3 






May 24 






1 


" 


May 2J 


2 

1 
1 

1 






9 


May 26 












May 31 












June 1 








I 


June 2 


















Total 


25 


1 


28 


3 1 


9 



Sixty-seven larvae were removed from the screen and cotton cloth 
between May .20 and June 2. The wind data given in the table were 
taken on the island, but comparison was also made with the records 
taken at Plum Island, Mass., 13^ miles to the southwest. It was 
thought that the air currents on the shore of the mamland where 
most of the small larvae were picked up would be much changed from 
their course before reaching the islands, but onl}" slight differences 
were noted by the two observers during the period. 



14 BULLETIN 273, U. S, DEPARTMENT OF AGEICULTUEE. 

It will be noted, according to the records taken on Lunging Island, 
that nine larvae came from the southwest, that is, from Plum Island, 
13^ miles away. The weather records at the latter place indicate 
that conditions were such tliat at least 18 of those caught on the 
screen at Lunging Island came from Plum Island, or more distant 
points in that dhection. 

Tliirteen and one-half miles is the maximum record for distance 
that larvae have been carried by the wind in all experiments thus far 
conducted by us, yet it is probable that the limit has not been reached. 
The locations for securing such records, together with suitable con- 
ditions with reference to infestations, are rare. 

DISPERSION EXPERIMENTS ON THE HILLS OF NEW HAMPSHIRE IN 1913 

AND 1914. 

In the scouting operations conducted by Mr. L. H. Wortliley in the 
outside territory infested by the gipsy moth, numerous infestations 
were bemg found on hilltops. It could not be ascertained whether 
this spread was the residt of the wind, vehicles, or other possible car- 
riers — man or animals. These hills contained woodlands, orchards, 
pastures, mowings, and roads over which there was more or less 
travel, making spread possible artificially. Thinning was practiced 
in these infestations, egg clusters were creosoted, and bands of 
tanglefoot were placed on the trees to keep the first-stage cater- 
pillars hatching near the ground from ascending the trees, thereby 
decreasing their chances of spread by the wind. 

To investigate the source of these hiUtop infestations, one hill was 
selected in each of four towns in New Hampshire, namely, Andover, 
Henniker (PI. IV, fig. 2), Hillsboro, and Troy, and large screens 
erected thereon as traps for the small caterpillars. (See also Plate 
VII.) It seemed desirable to know if these colonies were the result 
of windspread, and whether caterpillars were being carried from hill- 
top to hiUtop, valley to hilltop, or vice versa, so that scouting and 
control methods could be changed accordingly. 

The screens were constructed of f-inch mesh poultry wire 3 feet 
wide. This was stapled to posts set in the form of a T. The 
posts were about 12 feet high and guyed with No. 13 wire. The 
wire was fastened in two widths, one above the other, making a 
screen surface 6 feet wide. The top selvage ranged from 10 to 12 
feet from the ground owing to the level of the land. The screens 
were erected with one wing 35 feet long, facing the north and south, 
and another, 40 feet long, facing east and west. The total number 
of square feet exposed to the winds in each screen was 450. 

There were known infestations one-tliird to two miles in all directions 
from the screens in the foregoing towns, but negative results were 



DISPERSION OF GIPSY-MOTH LAEV.^ BY THE WIND. 15 

secured on those at Hiilsboro and Troy, N. II., the infestations in 
the neighborhood of which were fewer and at longer distances. 

In 1912 several large gipsy-moth colonies were found in Andover 
and Henniker, N. H. On Beech Hill, Andover, about one-tlm^d of a 
mile from where the screen was erected, over 30,000 larvae were 
destroyed in the summer of 1912, This colony and surroundings 
were carefully treated, so that the infestation was nearly extermi- 
nated in 1913 and 1914. AU the smaller colonies found in the town 
also received thorough treatment. Similar conditions prevailed in 
Henniker. 

The screens were examined at periods during the dispersion season 
of 1913 and 1914. No positive results were secured during the first 
year, but one hving larva was removed from the Andover screen 
May 27, 1914, at 2 p. m. 

May 26, 1914, a dead larva was removed from the Henniker screen 
and a living specimen June 13, together with the molted sldn of a 
second-stage larva. It is difficult to state from which direction the 
first larva was blown, but the second came from the northwest or 
west as the wind blew from those directions during the two days 
previous. 

The 3 first-stage larvae caught on the Andover and Henniker 
screens in 1914 proved conclusively that the dispersion among the 
hiUs is brought about most extensively by the wind. Tliis is more 
emphatic when one considers the small air space covered by these 
traps and the small sources of infestation in these localities. 

ALTITUDE EXPERIMENT WITH AVIATION OF SMALL CATERPILLARS. 

At the close of the season's work in 1913, after securing some fair 
records on the distance that larva? are borne by the wind, it seemed 
advisable to get data on the possible altitude they reach during their 
transportation. After numerous inquiries and investigation a suit- 
able place for such an experiment was found in Merrimac, Mass. 
(PL VII). This consisted of the standpipe (PL V, fig. 1) for the stor- 
age and pressui'e of the town water. It is located on a small hill 240 
feet above sea level, and permission to erect a small wire screen on 
the top of the tank was obtained from the selectmen of the town. 

The tank was 55 feet high from the level of the summit of the hill 
and a screen of f -inch mesh poultry wire was stapled to upright 2 by 4 
posts 5 feet long. The top selvage of the wire (PL V, fig. 2) was 5 
feet above the top of the tank, totaling 60 feet above the ground. 
The screen was 36 feet long and contained 144 square feet, while the 
tank was 40 feet in diameter, allowing ample space for the examiner 
to get around the ends. It was set up so that the sides faced the east 
and west. 



16 



BULLETIN" 273^ U. S. DEPARTMENT OF AGRICULTLTEE. 



Near the tank were a few low trees consisting of white pine and 
gray birch; these were cleaned of egg clusters and the trunks tangle- 
footed in order to prevent the larvae resulting from overlooked egg 
clusters getting into the tops of the trees. The country about this 
hill on all sides is generally infested (PI. VI), so that almost all winds 
tempered to 50° F. or above bore caterpillars. The weather data 
used for comparison with the daily catch here was taken at Plum 
Island, about 10 miles east. 

Table VI.- — Dates and numbers of caterpillars removed from screen at Meirimac, Mass., 
in 1914; also general direction of the loind during the period. 



Date and time removed. 


Number 
borne by 
west winds. 


Number 

borne by east 

and south 

winds. 


Direction of wind at time of examinations and a 
few hours previously. 


May 19, p. m 


1 9 
22 

'% 

8 

32 
2 

(') 

3 12 


2 

n 

1 






NW. and W., 8 a. m. to 5 p. ra. 


May20, p.m 


NW. and W., May 19, 8 a. m., to May 20, 2 p. m. 


May21 


May 22, p. m 


44 







NE., E., and SE., May 20, 3 p. m., to May 22, 5 

p. m. 
W., NW., and SW., May 23, 8 a. m., to May 27, 


May 23, p. m 




10 a. m. 
Do. 


Maj' 25, p. m 


Do. 


May 26 




May 27, p.m 






Do 


May 27, p. m 


Changed to S., May 27, 11 a. m., to 5 p. m. 
W. and NW., May 28, 8 a. m. to 5 p. m. 




May 29 


Maj' 30, p. m 





SW. and W., May 30, 8 a. m., to June 1, 11 a. m. 


May 31 


June 1, p.m 






S. and SE., June 1, 12 m. to 5 p. m. 

W. and NW., June 5, 8 a. m., to June 6, 5. p. m. 






Total 


91 


50 









1 Some of these larvse were caught before thi; date, as 7 were dead on removal. 

2 No examination. 

3 Number accredited to different winds estimated owing to changes in direction. 

One hundred and forty-one larvfe were trapped on this screen of 
144 square feet between May 19 and June 2, inclusive. A few of these 
undoubtedly were blown on before May 19, as seven of the nine were 
dead on removal, indicating that the aviation of the small larvae 
began probably two or more days earlier in Merrimac than along the 
seacoast. 

With apparently an equal infestation on all sides of this screen 
one-half mile or more distant, almost twice as many larvae were 
trapped as a result of prevailing winds from the west as from the east. 

The data secured in this experiment indicate that all wmds during 
the day in a section generally infested bear caterpillars excepting the 
north, which was not recorded during this period. Considering that 
practically one larva was caught per square foot 300 feet above sea 
level, it is only by conjecture that we can estimate the maximum 
height reached by them and the length of time they remain suspended 
under average conditions. It is a known fact that large numbers of 



Bui. 273, U. S. Dept. of Agriculture. 



Plate V. 



/ 



...4*0-^ -*-'^^ ••' ^ 



"■^^'^^fl'^ii 




^^^^^^^^g^^M^^^i^^i^ii 



jg ..--'it. : •; ^r ^-7 - %i.t ' \fei. 




Fig. 1.— Showing Standpipe, Merrimac, Mass. Arrow Points to Screen Trap 
ON Top. (Original.) 




Fig. 2.— Screen on Standpipe, Merrimac, Mass., at Close Range, where 141 
Larv^ were Caught During May and June, 1914. (Original.) 

SCREEN TRAP FOR WIND-BLOWN GIPSY-MOTH LARV/E, MERRIMAC, 

MASS. 



Bui. 273, U. S. Dept. of Agriculture. 



Plate VI 




DISPEESION OF GIPSY-MOTH LAEV^ BY THE WIND. 17 

isolated infestations are scattered in hill and dale over 19,378 square 
miles of the New England States (PI. VII), excepting Vermont,* and 
a comparison of such information with the foregoing data at once 
suggests the source of practically all spread of this species. 

OBSERVATIONS ON WIND DISPERSION AT SALISBURY BEACH, MASS., 

IN 1913 AND 1914. 

Salisbury Beach, owing to its separation by extensive marshes from 
infested woodlands and to the hmited amount of favorable food plants 
for gipsy moths thereon, was selected as a desirable location to be 
cleaned up and watched for reinfestation. The south end of the 
beach (PI. II), IJ miles in length, was scouted and the egg clusters 
were creosoted in 1913 and 1914. Beach plum was the predominant 
shrub growing on the sands and was not fed upon by the caterpillars. 
Bayberr}^, wild rose, wiUow sprouts, balsam poplar, and other small 
growth thrived to a certain extent and are favored food plants. 

The scouting in 1913 residted in the finding of 144 egg clusters 
distributed over the beach in a few clumps of shrubbery. The con- 
trol work was followed up during the summer by frequent examina- 
tions for caterpillars, which resulted in their discovery in seven or 
more places other than where egg clusters were located. From 
one to six caterpillars were found in small isolated clumps of bay- 
berry and wild rose in no less than six spots near which there were no 
egg clusters. These patches of favorable food afforded good traps 
for the newly hatched caterpOIars, which were being carried from the 
infested woodlands 1 mile to the west, as did the tanglefooted screen 
on which such large numbers were caught the same year. 

Seventy-seven egg clusters were found and creosoted in 1914 in the 
same area as was scouted in 1913. Thus it will be noted that there 
were slightly more than one-half the number of egg clusters found in 
1914 as in 1913, in spite of the rigid control measures practiced durmg 
the former year. The location of the beach with respect to the 
mfested woodland across the marshes was ideal for heavy reinfesta- 
tion each year, and this condition prevails in apple orchards, wood- 
lands, and shade trees that are cleaned within the gipsy moth infested 
area and become reinfested annually by means of the wind. 

OBSERVATIONS ON ISOLATED TREES AND YOUNG APPLE ORCHARDS 

FOR REINFESTATION. 

Twelve isolated trees in the midst of cultivated fields and mowings 
were selected in the early spring of 1914; these were cleaned of egg 
clusters, trunks tanglefooted, and later examined for reinfestation b}'' 
the wind. These trees were selected in towns about Merrimac, Mass., 

1 During the winter of 1914-15 a few small infestations were discovered in Vermont. 



18 BULLETIN 273^ U. S. DEPAETMENT OF AGRICULTUEE. 

where there was a general infestation. Some of thcni were later dis- 
carded owing to the discovery of overlooked egg clusters that had 
hatched. On the trees retamed there were from 2 to 8 and in one 
case 11 large caterpillars above and below the tanglefoot, indicating 
that there was reinfestation by the wind. The top of a medium to 
large sized apple tree would offer more resistance to the wind than 
did the screen on the Merrunac standpipe, upon which was lodged 
approximately one first-stage caterpillar to every square foot of wire 
exposed. 

Some further observations confirming these conclusions were made 
by Mr. C. E. Hood in July, 1914, in two young apple orchards in 
Merrimac (PL VI) and West Newbury, Mass. These orchards were 
2 and 4 years old, respectively, and clean cultivation was practiced 
m them, A large number of the trees were examined in the center 
of these orchards, which were in some cases 500 yards from the 
nearest mfestations on larger trees. Thirty-four large larvag were 
found in selected areas of the two orchards, not more than one of 
which appeared on a single tree. No egg clusters could be found, 
and it was concluded that the infestation was due to windspread. 

Mr. J. V. Schaffner, jr., has also reported a similar incident from 
Dover, Mass. 

SMALL LARV^ BLOWN INTO THE OCEAN ANNUALLY FROM INFESTED 
WOODLANDS NEAR THE COAST. 

At the rate of 266 first-stage larvse caught on 450 square feet of 
tanglefooted wire at Salisbury Beach in 1913 (being located 1 mile 
from the nearest infested woodland), a basis is given for estimating 
the huge numbers borne into the ocean each year. At the same 
ratio a continuous screen 1 mile long and 6 feet high would have 
caught 18,726 larvae. Judging from the altitude, 300 feet above sea 
level, where quantities were caught at Merrimac, Mass., it is apparent 
that this number should be fifty times as much, or 936,300 per mile. 
There is now upwards of 450 miles of coast line infested in New 
England (PL VII), and figuring that general spread by wind occurs 
over one-half of this distance, the ocean swallows up annually over 
210,000,000 small larvse. The number is probably much greater 
than is here indicated, as it is not known how many of the small 
larvae passed through the wire meshes of the screen which is used as 
a basis for these figures. 

These calculations, which are partly theoretical, serve to indicate 
what might have been the result with regard to the area infested had 
the moth first been introduced 100 miles farther westward than Med- 
ford, Mass. It also emphasizes the necessity of keeping this moth 
confined to New England territory, if rapid and general spread over 
the United States is to be prevented. 



DISPERSION OF GIPSY-MOTH LARV^ BY THE WIND. 



19 



FEEDING OF LARV^ PRIOR TO DISPERSION BY THE WIND. 

Several of the first-stage caterpillars of various sizes caught on the 
screens during 1913 and 1914 were selected and examined for the 
presence of plant cells in the alimentary tract. As aU caterpillars 
blown any reasonable distance by the wind are newly hatched, first- 
stage specimens, it is impossible to ascertain from a superficial ex- 
amination which have taken food and which have not. Before the 
examinations were made it was necessary to fix the material, stain 
with eosin and methylene blue, section with a microtome, and mount 
on slides, and this work was performed at Bussey Institute, Harvard 
University, under the direction of Dr. II . W. Glaser of the Bureau of 
Entomology. 

Caterpillars were selected diu'ing the two seasons which had been 
borne by the wind a distance of 1, 2, and 6 or more miles, respec- 
tively, from the nearest source of infestation. Results were as 
follows : 



Table VII. — Percentages of small caterpillars having Jed which were caught on screens 

during 1913 and 1914- 



Year. 


Locality and distance carried by wind. 


Number of 

caterpillars 

that had 

fed. 


Number of 

caterpillars 

that had 

not fed. 


1913 


Salisbury Beach, Mass., 1 mile from infested woodland 


13 
1 
2 

7 



7 


1914 


Isles of Shoals, N. H. Infestation in brushland aroimd screen 

Plum Island, Mass.; 2 miles from infested woodland. ... 



5 




Isles of Shoals , N . H .; 6 miles or more from infestation on the main- 
land to the westward 


8 




Merrimac, Mass.; J to 1 mile from heavy infestation in all directions. . 
Total 


2 




23 


22 









Of the 45 small caterpillars prepared and exammed during the two 
years that experiments were conducted, 23, or 51 percent, had con- 
sumed a very small amount of food, while the remainder, 40 per 
cent, -showed no signs of it. 

COMPARISON OF WEATHER DATA BETWEEN PROVIDENCE, R. I., AND 
AMHERST, MASS., WITH REFERENCE TO DISPERSION IN 1913. 

The period m which first-stage larvae were borne by the wind in 
1913 in eastern Massachusetts was from May 9 to June 5, inclusive. 
After comparing the hourly wind direction from 7 a. m. to 6 p. m. 
when there was no ram and the tem|3*>rature was 50° F. or above at 
Providence, R. I./ and Amherst, Mass.,^ one notes a slight difference 
in the total wind movement in the various directions. For mstance, 
in Providence the wind blew from the northwest 92 hours, from the 

1 The weather records at Providence were secured from the oflBce of the U. S. Weather Bureau, and 
those at Amherst from the Experiment Station. 



20 BULLETIN 273, U. S. DEPAETMENT OF AGKICULTUKE. 

aortli 17, from the northeast 22, from the east 3, from the southeast 
51, from the south 37, from the southwest 1, and from the west 9 
hours duruig the foregomg period. In Amherst, Mass., it blew for the 
same period from the northwest 50 hours, from the north 51, from 
the northeast 9, from the east 2, from the southeast 30, from the south 
31, from the southwest 3, and from the west 46 hours. 

Providence was first found mfested by the gipsy moth m 1901, 
and during the scouting season of 1913-14 egg clusters were found 
as far west as Woodstock, Pomfret, and Brooklyn, Conn. — a distance 
of 36 miles, or an average spread of 3 miles each year. It is apparent 
that this general infestation was not accomplished by direct east 
wmds, as there are few recorded each year at the proper period, but 
by a combmation of northeast and southeast winds transporting the 
larvae m a southwesterly and northwesterly direction from 1 to 10 
miles, thus gaining an average of 3 miles each year directly west. 

Although this insect has not yet reached Amherst, Mass., in its 
general sweep across the country, it occurs withm a few miles to the 
eastward. A perusal of the wmd records for the dispersion period 
of 1913 shows tlu'ee times as many hours of north winds and about 
one-half as many northeast and southeast winds combined as are 
recorded m Providence, R. I. The total movement of northwest 
and west wmds, which blow the larvae back into the infested terri- 
tory each year, is practically the same in the two locahties. 

From this data it appears that the increase m the amount of north 
wmds and the decrease in combmed northeast and southeast winds 
at Amherst, when compared with the wind records at Providence, 
may result in a somewhat more rapid southwestern advance of the 
insect if it becomes established in the Connecticut Valley. More 
rapid southern and western spread is likely if the infestation reaches 
the Central States! 

SPREAD OF THE GIPSY MOTH IN NEW ENGLAND. 

The gipsy moth was introduced at Medford, Mass. (PI. VII), m 1869, 
from which pomt it has spread gradually over large areas m Massa- 
chusetts and other New England States, excepting Vermont.^ Small 
mfestations have also been located in New York, New Jersey, and 
Ohio, but these colonies are fast being exterminated. Extensive 
efforts to prevent spread have been carried on in Massachusetts by 
the State since 1890, with suspension of appropriations and efforts 
only from 1900 to 1905. Other mfested States have appropriated 
smaller amounts which have aided in the suppression work. Con- 
gress began making appropriations in 1906, and these aimual sums 
have been expended to prevent spread and help control of the gipsy 
moth and the brown-tail moth. 

' See, however, footnote on p. 17. 




DISPERSION OF THE GIPSY MOTH 



NEW ENGLAND 

AND 

AREA QUARANTINED - 1914. 



DISPEKSION OF GIPSY-MOTH LAEV^ BY THE WIISTD. 



21 



Table VIII is here presented to show the annual advance of the 
moth before and after control was attempted. This indicates that 
the winds are chiefly responsible for the present conditions. 

Table VII T. — Spread of the gipsy moth in various directions htj series of years from five 
years after its introduction at Medford, Mass., to 1914. 



Periods of years. 


NE. 


N. 


NW. 


W. 


S\V. 


S. 


SE. 


Average spread 

per year by 

periods. 


1875-1890 


Miles. 
15 
5 
27 
41 
114 


Miles. 
10 
4 
11 
(iO 
16 


Miles. 
5 
5 
12 
25 
28 


Miles. 
10 
4 
10 
19 
15 


Miles. 
G 
4 

12 
15 
24 


Miles. 
4 
5 
14 
16 
26 


Miles. 
3 
4 
62 
11 



Miles per year. 
0.5 


1891-1899 




1900-190S 


3.5 


1906-1909 


6.7 


1910-1914 


6.4 






Total 


202 


101 


75 


58 


61 


65 


80 






2.3 




















Average spread per year in 


5 


2.5 


1.9 


1.5 


1.5 


1.6 


2 









It will be noted that the spread from the original center was very 
slow, averaging only 0.5 of a mile per year up to the beginning of the 
campaign in 1890. It was then held in control for a period of about 
nine years, during which time there was very little advance into new 
territory. The conditions in the old infested area were also much 
improved. This shows the necessity for keeping the moth under 
complete control if windspread is to be prevented. During the 
period from 1900 to 1905, when no work was being done, the moths 
spread at the rate of 3.5 miles per year. This had increased to 6.7 
miles per year from 1906 to 1909, but this ratio has decreased to 
some extent in the last period up to 1914, inclusive. 

The greatest distance gained in various directions has been to the 
northeast, an average of 5 miles per year for 40 years, which is the 
result of the favorable southwest winds. The combination of south- 
east and southwest winds during the dispersion period has carried 
the larvae northward at the rate of 2.5 miles per year. The spread 
to the west, southwest, and south was accomplished at a slower rate, 
owing to the less favorable winds blowing; in those directions. 



SUMMARY. 

In 1913, as a result of the several experiments conducted by using 
tanglefooted screens and cloth for traps, there were caught on 977 
square feet 289 first-stage larvae which had been borne by the wind 
one-eighth to 1 mile or more. In 1914 there were removed from 
1,614 square feet of sticky surface 346 larvfe which had been blown 
from one-eighth to 13^ miles or more, as verified by the wind records 
taken at or near those points. Three larvae were also taken from 
two large screens on the hills in New Hampshire during 1914. 



22 BULLETIN 273, V. S. DEPARTMENT OF AGEICULTURE. 

Considering the great numbers of lai'vse taken in these experiments, 
there can be no doubt that the wmd is ahnost wholly responsible for 
the general spread of this insect in New England, notwithstanding 
the fact that many of the former pubhcations teem with explanations 
of possible accidental or artificial spread by man and animals. The 
recent establishment by the Federal Horticultural Board of a quaran- 
tine on lumber products, Clu-istmas trees, nursery stock, and stone 
moving from the infested territory, until inspection has been made, 
has greatly relieved the danger of a general distribution of the gipsy 
and brown-tail moths over the United States, but the sources of dis- 
persion of the gipsy moth by the wmd can only bo lessened by the 
effectiveness of the parasites and predaceous enemies, together with 
hand methods of control. To prevent continual spread by the wmd 
into new territory the badly infested areas near the border must be 
brought mider control either by natural enemies, or hand methods, 
or both. Natural enemies, however, are now playing an important 
role in the control of this insect in the greater area of the inside 
infested territory. 

The larvae are sufficiently active and allow themselves to be trans- 
ported by the wmd at temperatures of 55° F. and above, and have 
been caught at wind velocities varymg from 2 to 23 miles per hour, 
although more active spread takes place when the temperature 
ranges'from 65° to 85° F. and when the velocity reaches 8 miles or 
more per hour. Larvte are removed from their support and carried 
by sudden gusts of wind, whether they spin or not, when the tempera- 
ture reaches 50° to 55° F., at which temperatures they often start 

crawling. 

The records also show that larvae have been caught at times when 
winds were blowmg from all du-ections except the north— only a very 
few coming from the east, but the location of the screens along and 
near the coast materiaUy affected this condition. By far the larger 
numbei-s were borne by combuiations of the west winds as indicated 
on the screen at Merrimac, Mass., wliich was surrounded by a general 
infestation. 

The general progress of the species since its estabhshment at 
Medford, Mass., at the rate of 5 miles per year to the northeast and 
at the rate of 3 miles per year westward from Providence, R. I., since 
its first appearance there in 1901 tends to verify the data that have 
been collected in connection with the screen experiments. 

BIBLIOGRAPHY. 

1893 Wachtl und Kornauth. Beltrage zur Kenntniss der Morphologie, Biologie 
und Pathologie der Nonne (Psilura monacha). In Mittheilungen aua dem 
forstlichen Versuchsvesen Osterreichs, v. 16, 38 p., 3 pi., 8 fig. 

1894. Cholodkovsky, N. Ueber die sogenannten "Aerophore" der Nonnenraupe. 
In Forst-naturw, v. 3, no. 5, p. 240-243, 1 fig., May. 



DISPERSION OF GIPSY-MOTH LAEV^ BY THE WIND. 23 

1896. FoRBusH, E. H., and Fernald, C. H. The Gipsy Moth. (Rpt. Mass. Bd. 

Agr.), 495+h'iii p., 66 pL, 37 fig. 

1897. Ingenitzky, I. Zur Kenntniss der Driisenhaare der Noimenraupe {Ocncria 

Monacha L.). In Horae Soc. Ent. Ross., v. 30, p. 129-134, 1895-'96. 

1912. EscHERicH, K. Die Bedeutung der "aerostatischen " Haare der Spiegelraupe. 

In Naturwissenschaftliche Zeitschrift fiir Forst- und Landwiitschaft, v. 10, 
no. 2, p. 82, February. 

1913. Burgess, A. F. The Dispersion of the Gipsy Moth. U. S. Dept. Agr., 

Bur. Ent., Bui. 119, 62 p., 16 pi., 6 fig. 

1913. Riley, Wm. A. The so-called aerostatic haii-s of certain lepidopterous larvae. 

In Science, n. s., v. 37, no. 958, p. 715-716, May. 

1914. Shcherbakoa\ T. C. Observations on the gipsy moth (Lymantria dispar L.) 

Translation from the Russian. In Proc. Mus. Nat. Hist. Taurican State 
Zemstvo, a-. 3, 1914. 



WASHINGTON : GOVEBNMENT PRINTING OFFICE : 1915 



Syracuse, N. Y. 

PAT. IAN. 21, 1 90S 



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